ro. FRICTION GEARING.
Almost noiseless and n on -vibrating.
Advantage of slip when shocks are
Useful for high speeds.
Frictional loss about the same as
for belt driving to shafting, but
comparatively small with one pair of
wheels. Unequal wear.
Large pressure on bearings ; de-
creased in nest gearing.
ii. COMPRESSED-AIR TRANSMISSION.
Of great value for long-distance
transmission in close workings.
Better than hydraulics when high
speeds are required in piston motors.
Loss by cooling varies from 70%
under bad conditions to 20% with
re-heating and air injection.
Loss per mile by friction about 5°/0.
12. HYDRAULIC (WATER
Suitable for Jong distances. More j
especially useful for intermittent de-
mand in power distribution, and the
concentration of immense power by
Inertia an advantage sometimes, as
in riveting machines.
Losses slight if low velocities are
taken, say I5°/0 in usual machines;
5°/o per mile due to friction in pipe.
Unsuitable for continuous work.
Uneconomical with high velocities
and reversible motion, on account of
shock due to inertia. (Damage ob-
viated by relief valves.)
Velocity should be kept down to 4
or 6 ft. per second usually, and slow
moving rams adopted, necessitating
Piston engines run at 60 or 80 ft.
per m. but are usually wasteful.
13. ELECTRICAL TRANSMISSION.
Especially suitable for long dis-
Wires may be conducted in any
No moving parts in line of trans-
Easy subdivision of power.
May be stored by secondary cells.
Loss in line varies as the square of
the current used (C2 R): hence high
voltage is adopted for long lines,
giving an economic loss of from 5%
to 40% in the line.
Loss in dynamos from 5% to 20%
each, of the energy intrusted to them.
Storage cells, being heavy, a*e
not really suitable for transportation
purposes. Loss in charging and
discharging, say 50%
(See Appendix //., p. 875, and Appendix III,, p. 928.)